1. Field of the Invention
The disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device including a light-emitting diode (LED) light source.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are most widely used for monitors of notebook computers, monitors of personal computers and televisions due to excellent moving images and high contrast ratio. LCD devices use the optical anisotropy and polarization properties of liquid crystal molecules of a liquid crystal layer to produce an image.
An LCD device includes two substrates spaced apart and facing each other and a liquid crystal layer interposed between the two substrates. The alignment direction of the liquid crystal molecules is controlled by varying the intensity of an electric field applied to the liquid crystal layer, and the transmittance of light through the liquid crystal layer is changed.
The LCD devices require an additional light source because the LCD devices are not self-luminescent. Therefore, a backlight unit is disposed at a rear side of a liquid crystal (LC) panel and emits light into the LC panel, whereby discernible images can be displayed.
Backlight units include cold cathode fluorescent lamps (CCFLs), external electrode fluorescent lamps (EEFLs), and light emitting diodes (LEDs) as a light source. Among these, LED lamps have been widely used due to their small sizes, low power consumption, and high reliability.
FIG. 1 is a cross-sectional view illustrating a liquid crystal display (LCD) module including LEDs as a light source according to the related art.
In FIG. 1, the related art LCD module includes a liquid crystal panel 10, a backlight unit 20, a support main 30, a top cover 40 and a cover bottom 50.
The liquid crystal panel 10 displays images and includes first and second substrates 12 and 14 facing and attached to each other with a liquid crystal layer (not shown) interposed therebetween. Polarizers 19a and 19b are attached at front and rear surfaces of the liquid crystal panel 10 and control the polarization of light.
The backlight unit 20 is disposed at a rear side of the liquid crystal panel 10. The backlight unit 20 includes an LED assembly 29, a reflection sheet 25, a light guide plate 23 and a plurality of optical sheets 21. The LED assembly 29 is disposed at an edge of at least one side of the support main 30 along a length direction. The reflection sheet 25 is disposed over the cover bottom 50 and is white- or silver-colored. The light guide plate 23 is disposed over the reflection sheet 25. The plurality of optical sheets 21 are disposed over the light guide plate 23.
More particularly, the LED assembly 29 is disposed at a side of the light guide plate 23. The LED assembly 29 includes a plurality of LEDs 29a emitting white light and a printed circuit board (PCB) 29b on which the LEDs 29a are mounted.
Edges of the liquid crystal panel 10 and the backlight unit 20 are surrounded by the support main 30 having a rectangular frame shape. The top cover 40 covers edges of the front surface of t he liquid crystal panel 10, and the cover bottom 50 covers a rear surface of the backlight unit 20. The top cover 40 and the cover bottom 50 are combined with the support main 30 to thereby constitute one-united body.
FIG. 2 is a cross-sectional view of enlarging an area A of FIG. 1. In FIG. 2, the LEDs 29a are arranged along the side of the light guide plate 23 of the modularized LCD module, and the LEDs 29a are mounted on the PCB 29b to constitute the LED assembly 29. The LED assembly 29 is fixed such that light emitted from the LEDs 29a faces a side surface of the light guide plate 23, which the light is incident on. To do this, the cover bottom 50 has a side that is twice bent upward and inward and which is referred to as a bending portion 51. The LED assembly 29 is attached to the bending portion 51 by an adhesive material such as a both-sided sticky tape. The structure may be referred to as a side top view type.
Accordingly, light F emitted from the LEDs 29a is incident on the side surface of the light guide plate 23 and then are refracted toward the liquid crystal panel 10 inside the light guide plate 23. With light reflected by the reflection sheet 25, the light is changed to have uniform brightness and high qualities through the plurality of optical sheets 21 and are provided to the liquid crystal panel 10. Accordingly, the liquid crystal panel 10 displays images.
There is a gap G between the light guide plate 23 and the bending portion 51 of the cover bottom 50. Some of the light F emitted from the LEDs 29a are leaked through the gap G, and there is light leakage. This lowers the brightness and image qualities of the LCD device.